If you are wondering if the entire planets population will be evacuated, not in a million years would they bother.
Byrd,
While I agree that most of the catastrophes you responded to, other than the comet/asteroid strike are not likely to be planet killers, I do have to
disagree, at least partially, about volcanic eruptions:
Granted, we have not yet in recorded history seen an eruption that would significantly threaten the entire planet (Krakatoa and Santorini being the
largest eruptions in recorded history, both of them around 100 megatons output). These were locally completely devastating, but had minimal effect on
the planet overall, with the exception of some suspended matter in the stratosphere that provided spectacular sunsets for a few years each.
However, I would direct your attention to this thread:
www.abovetopsecret.com...
and this one:
www.abovetopsecret.com...
I would stress the destructive power of supervolcanos and supercalderas as being on a level that humanity in general is just not capable of truly
grasping.
The last really major super eruption occurred approximately 72,000 BC, with the Toba eruption. There are no reliable estimates on explosive yield for
this explosion, but it is estimated that it ejected over 2000 cubic kilometers of material (airborne!) from the ground. (By contrast, Mt St. Helens,
estimated at approximately 20 megatons yield, ejected less than 2 cubic kilometers of material, and loss of life was mitigated because the slope
failed on a slope facing away from population areas)
The Toba eruption wiped out so much of the human race that the effects have been traced through mitochondrial DNA (please read thread, very
interesting, and scary)
Of course, the supercaldera that is of immediate concern is Yellowstone, which last erupted 640,000 years ago. Although Yellowstone is not as large as
Toba, it would still have absolutely devastating consequences to the entire North American Continent. I would point out (through personal experience
in field studies) that the last Yellowstone eruption deposited layers of volcanic tuff
in El Paso Texas (!!!) over 20 feet thick, and layers of
the same material
in Austin Texas (!!!) over 12 feet thick.
As far as evacuation from such threats, I do know that there has been a concerted effort since the 1980s to construct "Phase III" bunkers, 10s of KM
deep in the ground, survivable from direct nuclear strikes. In addition, there IS an operational base on the moon, served by USAF X Craft from both
Alaska and Pine Gap Australia. I would imagine these facilities to be the most logical evacuation points for the nations elite.